Electro-optic liquid level sensing system for aircraft beverage brewing

ABSTRACT

The electro-optic liquid level sensing system detects a level of liquid in a container having an upper opening, such as for a server container of a beverage maker for a transport system, such as for aircraft, trains, trucks, buses and the like. A support housing mates with the upper opening of the container, and a primary liquid level sensor is mounted in the support housing for non-intrusively measuring the liquid level. A secondary liquid level sensor may be mounted in the support housing to sense a predetermined liquid level to prevent accidental overflows. Protective lenses may be placed in front of the primary liquid level sensor.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to liquid level detection systems, and moreparticularly, to a system to detect the liquid level in a servercontainer of a beverage brewing apparatus adapted for use on aircraft.

2. General Background and State of the Art

One conventional technique for determining the level of a liquid in avessel or container involves mechanically measuring the liquid levelwith a contact device such as a float indicator, dip stick or probewhich extends intrusively into the liquid to be measured. When suchtechniques are used for measuring liquid level in a server container ofa beverage brewing apparatus, such as a coffee brewing machine, thesetechniques require a sensing device to extend into the server containerto contact the liquid, which subjects the sensing device to damage whenthe server container is repetitively installed and removed from thebeverage maker brewing cavity.

One non-contact liquid level sensing technique for non-intrusivelydetecting the level of the surface of a fluid in a vessel utilizes alaser liquid level gauge that includes an optical unit in the top wallof the vessel. Reflections of an incident laser beam from the fluidboundary are focused by optics to a photodiode producing an outputsignal received by a control unit, which includes a phase detector forcomparing the phase of the modulation tone with that of the detectionsignal to produce a level indicating signal for display. Anothernon-contact liquid level sensing technique for measuring the volume ofliquid in a container utilizes an ultrasonic system. An ultrasonicsignal is emitted from the lid of the container, and is received by asensor subsystem located on the underside of the lid of the ultrasonicsystem. The ultrasonic system measures the level of liquid in thecontainer by determining the time the ultrasonic signals take to travelto and return from the surface of the liquid reflecting the ultrasonicsignals to the ultrasonic sensor subsystem.

Another liquid level sensing technique utilizes an opto-electronic levelsensor including a system with an infrared light emitting diode (IRED)and two silicon phototransistors. A first phototransistor monitors thelight reflected from the liquid, and the second phototransistor directlymonitors the IRED beam for power degradation or failure and providesinterrupt control as required. While the failure of the IRED can bedetected directly in this manner, failure of the first phototransistorcan go undetected, allowing an overflow to occur. A temperature sensorincluded with the liquid level sensor that extends intrusively tocontact the liquid is also vulnerable to being damaged by repeatedusage. Another inherent problem with this approach is that the lightemitting and sensing optical sensors are not protected from the steam,water condensation and accumulation of coffee residue, and frequentcleaning operations are required to keep the level sensing systemoperational, which is time consuming and expensive. Typical cleaning ofthe liquid level sensors requires inserting a cotton swab moistened withalcohol into the sensor ports, and clearing the sensor ports of lintfrom the cotton swab. Failure to perform these cleaning operationstypically results in uncontrolled overflows due to accumulation ofdebris and coffee residue on the light emitting and sensing opticalsensors. It would therefore be desirable to provide a liquid levelsensing device that is less prone to contamination.

Such conventional liquid level sensing systems also typically do notprovide any redundancies in the event that the primary sensing apparatusmonitoring the liquid level fails, either by internal failure or due tocoffee residue build up. Failure to detect the liquid level will resultin an overflow, which is not only inconvenient, but also dangerous forthe operator. During an overflow, very hot liquid typically comes out ofthe server and the beverage maker, and spills out, potentially burningthe operator attending the machine. It would therefore be desirable toprovide a backup liquid level sensing system for preventing accidentaloverflows in case of a malfunction of a primary liquid level sensingsystem. The present invention satisfies these and other requirements foraircraft galley systems.

INVENTION SUMMARY

Briefly, and in general terms, the invention provides for an apparatusfor detecting a level of a surface of a liquid in a container having anupper opening, such as for a server container of a beverage maker for atransport system, such as for aircraft, trains, trucks, buses and thelike.

In one presently preferred embodiment, the apparatus includes a supporthousing adapted to mate with the upper opening of the container, primaryliquid level sensing means mounted in the support housing fornon-intrusively measuring the level of the surface of the liquid in thecontainer; and secondary liquid level sensing means mounted in thesupport housing for intrusively sensing a predetermined level of thesurface of the liquid in the container for preventing accidentaloverflows in the event of a malfunction of the primary liquid levelsensing means.

In one aspect, the primary liquid level sensing means may be an opticalsensor device mounted in the support housing for non-intrusivelymeasuring the level of the surface of the liquid in the container, theoptical sensor device including a light emitting device for projectingincident light on the surface of the liquid in the container, and alight detecting device for detecting the incident light reflected fromthe surface of the liquid in the container. In one variation, theprimary liquid level sensing means may be an ultrasonic level measuringsystem, for example. In another variation, the primary liquid levelsensing means may include means for determining the level of the surfaceof the liquid in the container by determining a timed flow of liquidinto the container.

In another aspect, the secondary liquid level sensing means may includea pair of short fixed electrically conductive probes extending to apredetermined level in the container when the support housing is matedto the upper opening of the container.

In another current aspect, where the container and the liquid in thecontainer are electrically conductive, the secondary liquid levelsensing means may include a first retractable, electrically conductiveprobe pivotally mounted to the support housing and adapted to extend toa predetermined level within the container, and a second electricallyconductive probe adapted to contact the container, whereby electricalcontinuity between the first and second electrically conductive probesindicates that the level of the surface of the liquid in the containerhas reached the predetermined level within the container.

In another aspect, where the liquid in the container is electricallyconductive, the secondary liquid level sensing means may include firstand second retractable, electrically conductive probes pivotally mountedto the support housing and adapted to extend to a predetermined levelwithin the container, whereby electrical continuity between the firstand second electrically conductive probes indicates that the level ofthe surface of the liquid in the container has reached the predeterminedlevel within the container.

In another aspect, where the container and the liquid in the containerare electrically conductive, the secondary liquid level sensing meansmay include a retractable, electrically conductive probe pivotallymounted to the support housing and adapted to extend to a predeterminedlevel within the container, and means adapted to contact the containerto ground the container, whereby electrical continuity between theelectrically conductive probe and ground indicates that the level of thesurface of the liquid in the container has reached the predeterminedlevel within the container.

In another presently preferred embodiment, the invention provides for anapparatus for detecting a level of a surface of a liquid in a containerhaving an upper opening. The apparatus includes a support housingadapted to mate with the upper opening of the container, an opticalsensor device mounted in the support housing for non-intrusivelymeasuring the level of the surface of the liquid in the container, theoptical sensor device including a light emitting device for projectingincident light on the surface of the liquid in the container, and alight detecting device for detecting the incident light reflected fromthe surface of the liquid in the container, and protective lenses placedin front of the light emitting device and the light detecting device.The protective lenses may be permanently and hermetically secured on thesupport housing housing, or may be incorporated in the support housinghousing.

In another preferred aspect, each of the protective lenses have an outersurface that is inclined with respect to the vertical, to allowcondensation to flow off the protective lenses, and each of theprotective lenses has an outer surface that is inclined at about 53°with respect to the vertical, to allow condensation to flow off theprotective lenses. In another aspect, the protective lenses and thelight emitting device and the light detecting device defines a volume inthe support housing housing, which may be filled with a dry gas, avacuum, or a solid translucent material, for example.

In one aspect, the light emitting device is an infrared light emittingdiode, and the light detecting device is a phototransistor. In anotheraspect, the light emitting device is positioned in the support housingto project light at an angle that is about 37° off vertical when thesupport housing is mounted to the upper opening of the container. Inanother presently preferred aspect, the light emitting device and thelight detecting device are positioned in the support housing so as toproject and receive the incident light at an included angle of about74°.

In another preferred embodiment, the invention provides for an apparatusfor detecting a level of a surface of a liquid in a container having anupper opening, including a support housing adapted to mate with theupper opening of the container, and at least one primary retractableliquid level sensing probe pivotally mounted in the support housing formeasuring the level of the surface of the liquid in the container. Theapparatus may also further include a secondary liquid level sensingprobe fixedly mounted in the support housing for sensing a predeterminedlevel of the surface of the liquid in the container for preventingaccidental overflows in the event of a malfunction of the primary liquidlevel sensing means.

The present invention also provides for a method for detecting a levelof a surface of a liquid in a container having an upper opening, such asfor a server container of a beverage maker for a transport system, suchas for aircraft, trains, trucks, buses and the like. A support housingis provided that is adapted to mate with the upper opening of thecontainer, and a primary liquid level sensing means is mounted in thesupport housing for non-intrusively measuring the level of the surfaceof the liquid in the container. In one aspect, the primary liquid levelsensing means may be an optical sensor device mounted in the supporthousing for non-intrusively measuring the level of the surface of theliquid in the container, the optical sensor device including a lightemitting device, such as an infrared light emitting device, forprojecting incident light on the surface of the liquid in the container,and a light detecting device, such as a phototransistor, for detectingthe incident light reflected from the surface of the liquid in thecontainer. The light source is typically driven continuously during abrew cycle, but the method of the invention provides for pulsing powerto the light emitting device, allowing the system to turn the lightemitting device on for only a fraction of the time during which thebeverage maker is in operation, thus increasing the useful life of thelight emitting device, and/or reducing the power requirements. Althoughthe light detecting device typically continuously measures reflectedemitted light, the method of the invention similarly provides formonitoring the light detecting device only when the light emittingdevice is on, so that the liquid level can be detected at variousintervals.

The provision of protective lenses significantly improves protection ofnon-intrusive primary liquid level sensors such as light emitting andlight receiving devices from direct water condensation. In addition,water condensation forming on and above the lenses will run off theouter surfaces of the protective lenses, so that the lenses tend to becleaned from coffee residue during each brew cycle, requiring no specialcleaning of the lenses. Since the lenses are hermetically sealed orintegrally formed on the support housing housing, no coffee residue canbuild up between the non-intrusive primary liquid level sensors and thesupport housing housing. Therefore the optical system of the inventionavoids creation of “dirt traps” which are unacceptable on foodprocessing equipment.

The secondary intrusive backup liquid level sensing probes alsoadvantageously serve to prevent accidental overflows in case of amalfunction of the primary non-intrusive liquid level sensing device.The backup probes provide a high reliability system for preventingaccidental overflow, and operate in conjunction with primarynon-intrusive liquid level sensing system, so that if one of the liquidlevel sensing systems fails, the other will stop the brew cycle beforethe server overflows.

The operation of the backup probes takes advantage of the electricalconductivity of the liquid brewed in the server. The probes are mountedon the support housing housing, and rest above the surface of the liquidbrewed. Should the primary liquid level sensor fail to detect the liquidlevel, the liquid will continue to rise up to the backup probes, andwill provide an electrical path between the probes, and electricalconduction between the probes will be detected by a beverage makerdecision logic circuit, and the brew cycle will be stopped, preventingan overflow. In an alternative embodiment, a single probe may beutilized if the server is grounded in the sensor electrical circuit.

The backup probes are shorter than are typically used for a primarysensor, so that they do not contact the beverage during normal operationand are much less vulnerable to becoming damaged when the pot is removedor replaced. However, their length is sufficient to contact the beveragebefore an overflow can occur. The backup probes are much less vulnerableto being damaged during normal operation because the probes are mountedon a support housing which is raised above the server. The supporthousing is mobile and translates up and down above the server opening.When the support housing is in the “up” or “unlock” position, the servercan be inserted in and out of the brew cavity without touching thebackup probes, so that wear and tear of the probes is minimized. Whenthe support housing is lowered into the server opening in the “down” or“locked” position, the probes rest at a height adequate to preventaccidental overflows. In one aspect, the backup probes can be passivelymovable, such as by being pivotally mounted to the support housing so asto extend into the server container when the support housing is loweredinto the server opening while allowing the backup probes to pivot asnecessary when moved into and out of the server container. In anotheraspect, the backup probes can be configured to be actively movable,actively extending into the server container when the support housingmates with the server container, and actively retracting when thesupport housing is raised to the “up’ or “unlock” position from theserver container.

The backup probes can be used with any other primary liquid levelsystem, including, but not limited to infrared sensing, ultrasonicsensing, capacitive sensing, and retractable probes.

Other features and advantages of the present invention will become moreapparent from the following detailed description of the preferredembodiments in conjunction with the accompanying drawings, whichillustrate, by way of example, the operation of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of an apparatus for detecting a liquid levelin a container, according to the invention.

FIG. 2 is a schematic diagram of the apparatus for detecting a liquidlevel in a container of FIG. 1, shown mounted to a beverage maker.

FIG. 3 is a front view of a beverage maker with the apparatus fordetecting a liquid level in a container of FIG. 1 mounted to thebeverage maker, and a server container.

FIG. 4 is a front view of a beverage maker with the apparatus fordetecting a liquid level in a container of FIG. 1 mounted to thebeverage maker, with a server container placed in the beverage maker,with the brew handle shown in the up or unlocked position.

FIG. 5 is a front view showing the apparatus for detecting a liquidlevel in a container of FIG. 1 mounted to the beverage maker, with thebrew handle shown in the down or locked position, and the apparatus fordetecting a liquid level mated to a server container.

FIG. 6 is a bottom perspective view of the support housing of theapparatus for detecting a liquid level in a container of FIG. 1.

FIG. 7 is a top perspective view of the support housing of the apparatusfor detecting a liquid level in a container of FIG. 1.

FIG. 8 is a top plan view of the support housing of the apparatus fordetecting a liquid level in a container of FIG. 1.

FIG. 9 is a an enlarged cutaway sectional view of a portion of theapparatus for detecting a liquid level in a container of FIG. 1,illustrating an alternate lens design.

FIG. 10 is a schematic diagram of an alternate embodiment of anultrasonic apparatus for detecting a liquid level in a container,according to the invention.

FIG. 11 is a schematic diagram of another alternate embodiment of atimed apparatus for detecting a liquid level in a container, accordingto the invention.

FIG. 12 is a schematic diagram of another alternate embodiment of anapparatus for detecting a liquid level in a container, according to theinvention, with a secondary liquid level sensing device including aretractable probe and a second probe adapted to contact the servercontainer.

FIG. 13 is a schematic diagram of another alternate embodiment of anapparatus for detecting a liquid level in a container, similar to FIG.12, in which the second probe connects to ground.

FIG. 14 is a schematic diagram of another alternate embodiment of anapparatus for detecting a liquid level in a container, according to theinvention, with a secondary liquid level sensing device including a pairof retractable probes.

FIG. 15 is a schematic diagram of another alternate embodiment of anapparatus for detecting a liquid level in a container, according to theinvention, with a primary liquid level sensing device including a pairof retractable probes.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides for an apparatus for detecting a level ofa surface of a liquid in a container having an upper opening, such asfor a server container of a beverage maker for a transport system, suchas for aircraft, trains, trucks, buses and the like.

In a first embodiment illustrated in FIGS. 1-9, the present inventionaccordingly provides for an apparatus 20 for detecting a level of asurface of a liquid 22 in a container 24 typically having an upperopening 26 such as a server container of a beverage maker such as acoffee brewer 28 for a transport system (not shown), such as foraircraft, trains, trucks, buses and the like. The beverage makertypically includes an enclosure 30 including a heated platen or hotplate 32 on which the server container is seated in the beverage maker,and a brew handle lever 34 movable between an “up” or “unlocked”position in which the server container may be freely moved into and outof the beverage maker, and a “down” or “locked” position in which theserver container is locked in the beverage maker for brewing andreceiving the beverage. The beverage maker typically also includesvarious indicator lights and control switches indicated generally at 36as well as a brew switch 38.

The liquid level detecting apparatus includes a support housing 40,shown mated to the server container in FIGS. 1 and 5, and shown mountedto a retaining plate 41 moved by the brew handle lever in FIGS. 3-5.Referring to FIGS. 1 and 6-8, the support housing typically includes ashoulder 42 configured to mate with the upper opening of the servercontainer, and at least one opening 44 for introduction of liquid intothe server container from the beverage maker. The support housing mayalso include one or more mounting holes 46 for securing the supporthousing to the retaining plate. The support housing also includes angledports 48 for the optical sensing apparatus, as will be described furtherbelow, and ports 50 for one or more backup sensor probes shown in FIG.1, also described further hereinbelow.

Referring to FIGS. 1 and 2, in one preferred embodiment, a primaryliquid level sensing means 52 is mounted in the support housing fornon-intrusively measuring the level of the surface of the liquid in thecontainer. A secondary liquid level sensing means 54 is mounted in thesupport housing for intrusively sensing a predetermined level of thesurface of the liquid in the container for preventing accidentaloverflows in the event of a malfunction of the primary liquid levelsensing means. In a preferred aspect, the primary liquid level sensingmeans is an electro-optic level sensing apparatus including an opticalsensor device 56, including a light emitting device 58, such as aninfrared light emitting diode (IRED) for projecting incident light onthe surface of the liquid in the container, and a light detecting device60, such as a phototransistor, for detecting the incident lightreflected from the surface of the liquid in the container.

While the angle at which the light is projected and received withrespect to the vertical when the support housing is horizontally matedto the server container may be greater than 0° and less than 90°,generally the angle will be between about 10° and about 80° with respectto the vertical, depending on the spacing and dimensions of the lightemitting device, the light detecting device, the support housing and theserver container, as will be further discussed below. Referring to FIGS.1, 6 and 9, in one preferred aspect, the light emitting device ispositioned in the support housing to project light at an angle 62 thatis typically about 37° from perpendicular relative to the supporthousing and about 37° off vertical when the support housing ispositioned horizontally when mounted to the upper opening of thecontainer. The light detecting device is similarly positioned in thesupport housing to receive light at an angle 64 of about 37° fromperpendicular relative to the support housing housing, so that togetherthe light emitting device and the light detecting device are positionedin the support housing so as to project and receive the incident lightat an included angle 66 of about 74° when the support housing ishorizontally mounted to the upper opening of the container.

Referring to FIG. 10, in an alternate embodiment, the primary liquidlevel sensing means mounted in the support housing for non-intrusivelymeasuring the level of the surface of the liquid in the container may bean ultrasonic level measuring system 68. Referring to FIG. 11, in analternate embodiment, the primary liquid level sensing means mounted inthe support housing for non-intrusively measuring the level of thesurface of the liquid in the container may be a timer means 70 fordetermining the level of the surface of the liquid in the container bydetermining a timed flow of liquid into the container.

In one embodiment illustrated in FIGS. 1-4, the secondary liquid levelsensing means for intrusively sensing a predetermined level of thesurface of the liquid in the container includes a pair of short, fixedelectrically conductive backup probes 72 a, 72 b which take advantage ofthe electrical conductivity of the liquid brewed in the servercontainer. The fixed backup probes are mounted on the support housinghousing, and rest above the surface of the liquid brewed, extending to apredetermined level 88 of the liquid in the server container when thesupport housing is mated to the server container. Should the primaryliquid level sensor fail to detect the liquid level, the liquid willcontinue to rise up to the backup probes, and will provide an electricalpath between the probes, and electrical conduction between the probeswill be detected by a beverage maker decision logic circuit 74, and theflow of liquid into the server container will be stopped, preventing anoverflow. As is illustrated in FIG. 2, the decision logic circuit,typically implemented in a microcontroller, controls brew and faucetsolenoids 76, the heated platen 32, heaters 80, as well as light source58, and receives input from the primary liquid level sensing means viaconnector 61, and from the secondary liquid level sensing means viaconnector 63. For controlling filling and temperature of a water tank ofthe beverage maker, entirely apart from monitoring the liquid level ofthe server container, the decision logic circuit may also receive inputsfrom the control switches, the brew switch, an internal water tank levelsensor 82, and an internal water tank temperature sensor 84, for safetypurposes.

In another embodiment illustrated in FIG. 12, when the server containerand the liquid in the server container are electrically conductive, suchas when at least a portion of the server container is made of a metalsuch as stainless steel, for example, the secondary liquid level sensingmeans includes a first retractable, electrically conductive probe 86pivotally mounted to the support housing and adapted to extend to apredetermined level 88 within the container, and a second electricallyconductive probe 90 adapted to contact an electrically conductiveportion of the server container, whereby electrical continuity betweenthe first and second electrically conductive probes indicates that thelevel of the surface of the liquid in the container has reached thepredetermined level within the container. The second electricallyconductive probe may be a pivoting probe or a leaf spring contact, forexample. Alternatively, the second electrically conductive probe may bemounted on the support housing so as to contact the server containerwhen the brew handle lever is moved downwardly to a “down” or “locked”position.

In another embodiment illustrated in FIG. 13, when the server containerand the liquid in the server container are electrically conductive, suchas when at least a portion of the server container is made of a metalsuch as stainless steel, for example, the secondary liquid level sensingmeans includes a retractable electrically conductive probe 92 pivotallymounted to the support housing and adapted to extend to a predeterminedlevel 88 within the server container, and contact means 94 adapted forcontacting and connecting the server container to ground the servercontainer, whereby electrical continuity between the electricallyconductive probe and ground indicates that the level of the surface ofthe liquid in the container has reached the predetermined level withinthe container. The second electrically conductive probe may be apivoting probe or a leaf spring contact, for example. Alternatively, thesecond electrically conductive probe may be mounted on the supporthousing so as to contact the server container when the brew handle leveris moved downwardly to a “down” or “locked” position.

In another embodiment illustrated in FIG. 14, the secondary liquid levelsensing means for intrusively sensing a predetermined level of thesurface of the liquid in the container includes a first electricallyconductive probe 96 and a second electrically conductive probe 98, eachof which are movably mounted to the support housing and are adapted toextend to a predetermined level 88 within the container. In one aspect,the first and second electrically conductive probes may be pivotallymounted to the support housing so as to be able to be passively moved toavoid damage to the probes. In another aspect, the first and secondelectrically conductive probes may be configured to be actively movable,mechanically or electrically actively extending into the servercontainer when the support housing mates with the server container, andmechanically or electrically actively retracting when the supporthousing is raised to the “up” or “unlock” position from the servercontainer. Electrical continuity between the first and secondelectrically conductive probes indicates that the level of the surfaceof the liquid in the container has reached the predetermined levelwithin the container.

In another preferred aspect illustrated in FIGS. 1, 6 and 9, aprotective window or lens 100 a is placed in front of the light emittingdevice, and a protective window or lens 100 b is placed in front of thelight detecting device. The protective lenses are preferably permanentlyand hermetically secured on the support housing housing, such as by asealing compound 102 such as an epoxy compound, for example, althoughthe protective lenses alternatively may be incorporated in the supporthousing housing, such as by forming the support housing of material thatwould be transparent to the spectrum of light emitted and detected, suchas infrared light spectrum, for example. The advantage of this approachwould be to streamline manufacturing by eliminating the need to assemblethe lenses onto the support housing housing. Each of the protectivelenses preferably has an outer surface 104 that is inclined at an anglewith respect to the vertical, when the support housing is mountedhorizontally to the service container, to allow condensation andcontaminants to flow off the protective lenses. While the angle of thelenses with respect to the vertical may be greater than 0° and less than90°, generally the angle of the lenses should be sufficiently displacedfrom the horizontal to facilitate drainage of liquid and contaminantsfrom the lenses, and may, for example, be generally between about 10°and about 80°, with respect to the vertical. One convenient approach isto choose angles for the lenses that are perpendicular to the angles ofthe light emitting device and the light detecting device, but this isnot essential. In a preferred aspect, the protective lenses aretypically inclined at an angle of about 53° with respect to thevertical, when the support housing is mounted horizontally to theservice container. In another preferred aspect, a volume 106 definedbetween a protective lens and the light emitting device, and between aprotective lens and the light detecting device, is filled with a drygas, a vacuum, or a solid translucent material.

In another embodiment illustrated in FIG. 15, the invention provides foran apparatus 110 for detecting a level of a surface of a liquid 112 in aserver container 114 typically having an upper opening 116, such as aserver container of a beverage maker such as a coffee brewer describedabove. The apparatus includes a support housing cover 118 adapted tomate with the upper opening of the server container, and a primaryliquid level sensing means 120 including at least one primary liquidlevel sensing probe 122 pivotally mounted in the support housing formeasuring the level of the surface of the liquid in the container. Asecond primary liquid level sensing probe 124 may also be pivotallymounted in the support housing for measuring the level of the surface ofthe liquid in the container. A secondary liquid level sensing means 126is fixedly mounted in the support housing for sensing a predeterminedlevel 88 of the surface of the liquid in the container for preventingaccidental overflows in the event of a malfunction of the primary liquidlevel sensing means. In one embodiment illustrated in FIG. 15, thesecondary liquid level sensing means for intrusively sensing apredetermined level of the surface of the liquid in the containerincludes a pair of fixed electrically conductive backup probes 128 a,128 b which take advantage of the electrical conductivity of the liquidbrewed in the server container. The fixed backup probes are mounted onthe support housing housing, and rest above the surface of the liquidbrewed when the support housing is mated to the server container. Shouldthe primary liquid level sensor fail to detect the liquid level, theliquid will continue to rise up to the backup probes, and will providean electrical path between the probes, and electrical conduction betweenthe probes will be detected by a beverage maker decision logic circuitas described above, and the flow of liquid into the server containerwill be stopped, preventing an overflow.

It should be appreciated that any of the foregoing secondary systems maybe substituted for fixed backup probes for use in combination with anyof the foregoing primary liquid level sensing systems.

The present invention also provides for a method for detecting a levelof a surface of a liquid in a container having an upper opening, such asa server container of a beverage maker such as a coffee brewer for atransport system. Apparatus for detecting the liquid level is provided,including a support housing adapted to mate with the upper opening ofthe container, with a primary liquid level sensing means mounted in thesupport housing for non-intrusively measuring the level of the surfaceof the liquid in the container, and a secondary liquid level sensingmeans mounted in the support housing for intrusively sensing apredetermined level of the surface of the liquid in the container forpreventing accidental overflows in the event of a malfunction of theprimary liquid level sensing means. The primary liquid level sensingmeans comprises an optical sensor device mounted in the support housingfor non-intrusively measuring the level of the surface of the liquid inthe container, the optical sensor device including a light emittingdevice for projecting incident light on the surface of the liquid in thecontainer, and a light detecting device for detecting the incident lightreflected from the surface of the liquid in the container, as describedabove.

Typically, the light source, such as an IRED, for example, is drivencontinuously during the brew cycle. In the improved method of theinvention, the power to the light source is intermittently pulsed,allowing the system to periodically turn the light source on only afraction of the time, thus increasing the useful life of the lightsource, and/or reducing the power requirements. Reflected emitted lightmay be measured continuously with the phototransistor, but thephototransistor can be monitored only when the light source is on, sothat the liquid level can be detected periodically, at various desiredintervals.

While the specification describes particular embodiments of the presentinvention, those of ordinary skill can devise variations of the presentinvention without departing from the inventive concept

1-54. (canceled)
 55. Apparatus for detecting a level of a surface of aliquid in a container having an upper opening, the apparatus comprising:a support housing moveable between an upward unlocked position and adownward locked position, said support housing being adapted to matewith the upper opening of the container in said downward lockedposition; primary liquid level sensing means mounted in said supporthousing for non-intrusively measuring the level of the surface of theliquid in the container; and secondary liquid level sensing meansmounted in said support housing for intrusively sensing a predeterminedlevel of the surface of the liquid in the container for preventingaccidental overflows in the event of a malfunction of the primary liquidlevel sensing means.
 56. The apparatus of claim 55, wherein said primaryliquid level sensing means comprises an optical sensor device mounted insaid support housing for non-intrusively measuring the level of thesurface of the liquid in the container, said optical sensor deviceincluding a light emitting device for projecting incident light on thesurface of the liquid in the container, and a light detecting device fordetecting said incident light reflected from the surface of the liquidin the container.
 57. The apparatus of claim 55, wherein said primaryliquid level sensing means comprises an ultrasonic level measuringsystem.
 58. The apparatus of claim 55, wherein said primary liquid levelsensing means comprises means for determining the level of the surfaceof the liquid in the container by determining a timed flow of liquidinto the container.
 59. The apparatus of claim 55, wherein saidsecondary liquid level sensing means comprises a pair of short fixedelectrically conductive probes extending to said predetermined level insaid container when said support housing is mated to the upper openingof the container.
 60. The apparatus of claim 55, wherein the containerand the liquid in the container are electrically conductive, and saidsecondary liquid level sensing means comprises a first electricallyconductive probe movably mounted to said support housing and adapted toextend to a predetermined level within the container, and a secondelectrically conductive probe adapted to contact the container, wherebyelectrical continuity between said first and second electricallyconductive probes indicates that the level of the surface of the liquidin the container has reached the predetermined level within thecontainer.
 61. The apparatus of claim 55, wherein the liquid in thecontainer is electrically conductive, and said secondary liquid levelsensing means comprises first and second electrically conductive probesmovably mounted to said support housing and adapted to extend to apredetermined level within the container, whereby electrical continuitybetween said first and second electrically conductive probes indicatesthat the level of the surface of the liquid in the container has reachedthe predetermined level within the container.
 62. The apparatus of claim55, wherein the container and the liquid in the container areelectrically conductive, and said secondary liquid level sensing meanscomprises an electrically conductive probe movably mounted to saidsupport housing and adapted to extend to a predetermined level withinthe container, and means adapted to contact the container to ground thecontainer, whereby electrical continuity between said electricallyconductive probe and ground indicates that the level of the surface ofthe liquid in the container has reached the predetermined level withinthe container.
 63. Apparatus for detecting a level of a surface of aliquid in a container having an upper opening, the apparatus comprising:a support housing moveable between an upward unlocked position and adownward locked position, said support housing being adapted to matewith the upper opening of the container in said downward lockedposition; at least one primary liquid level sensing probe movablymounted in said support housing for measuring the level of the surfaceof the liquid in the container.
 64. The apparatus of claim 63, furthercomprising a secondary liquid level sensing probe fixedly mounted insaid support housing for sensing a predetermined level of the surface ofthe liquid in the container for preventing accidental overflows in theevent of a malfunction of the primary liquid level sensing means. 65.The apparatus of claim 64, wherein said secondary liquid level sensingmeans comprises a pair of short fixed electrically conductive probesextending to said predetermined level in said container when saidsupport housing is mated to the upper opening of the container. 66.Apparatus for detecting a level of a surface of a liquid in a servercontainer of a beverage maker for a transport system, said servercontainer having an upper opening, the apparatus comprising: a supporthousing moveable between an upward unlocked position and a downwardlocked position, said support housing being adapted to mate with theupper opening of the container in said downward locked position; primaryliquid level sensing means mounted in said support housing fornon-intrusively measuring the level of the surface of the liquid in theserver container; and secondary liquid level sensing means mounted insaid support housing for intrusively sensing a predetermined level ofthe surface of the liquid in the server container for preventingaccidental overflows in the event of a malfunction of the primary liquidlevel sensing means.
 67. The apparatus of claim 66, wherein said primaryliquid level sensing means comprises an optical sensor device mounted insaid support housing for non-intrusively measuring the level of thesurface of the liquid in the server container, said optical sensordevice including a light emitting device for projecting incident lighton the surface of the liquid in the server container, and a lightdetecting device for detecting said incident light reflected from thesurface of the liquid in the server container.
 68. The apparatus ofclaim 66, wherein said primary liquid level sensing means comprises anultrasonic level measuring system.
 69. The apparatus of claim 66,wherein said primary liquid level sensing means comprises means fordetermining the level of the surface of the liquid in the servercontainer by determining a timed flow of liquid into the servercontainer.
 70. The apparatus of claim 66, wherein said secondary liquidlevel sensing means comprises a pair of short fixed electricallyconductive probes extending to said predetermined level in said servercontainer when said support housing is mated to the upper opening of theserver container.
 71. The apparatus of claim 66, wherein the servercontainer and the liquid in the server container are electricallyconductive, and said secondary liquid level sensing means comprises afirst electrically conductive probe pivotally mounted to said supporthousing and adapted to extend to a predetermined level within the servercontainer, and a second electrically conductive probe adapted to contactthe server container, whereby electrical continuity between said firstand second electrically conductive probes indicates that the level ofthe surface of the liquid in the server container has reached thepredetermined level within the server container.
 72. The apparatus ofclaim 66, wherein the liquid in the server container is electricallyconductive, and said secondary liquid level sensing means comprisesfirst and second electrically conductive probes movably mounted to saidsupport housing and adapted to extend to a predetermined level withinthe server container, whereby electrical continuity between said firstand second electrically conductive probes indicates that the level ofthe surface of the liquid in the server container has reached thepredetermined level within the server container.
 73. The apparatus ofclaim 66, wherein the server container and the liquid in the servercontainer are electrically conductive, and said secondary liquid levelsensing means comprises an electrically conductive probe movably mountedto said support housing and adapted to extend to a predetermined levelwithin the server container, and means adapted to contact the servercontainer to ground the server container, whereby electrical continuitybetween said electrically conductive probe and ground indicates that thelevel of the surface of the liquid in the server container has reachedthe predetermined level within the server container.
 74. Apparatus fordetecting a level of a surface of a liquid in a server container of abeverage maker for a transport system, said server container having anupper opening, the apparatus comprising: a support housing moveablebetween an upward unlocked position and a downward locked position, saidsupport housing being adapted to mate with the upper opening of thecontainer in said downward locked position; at least one primary liquidlevel sensing probe movably mounted in said support housing formeasuring the level of the surface of the liquid in the servercontainer.
 75. The apparatus of claim 74, further comprising a secondaryliquid level sensing means fixedly mounted in said support housing forsensing a predetermined level of the surface of the liquid in the servercontainer for preventing accidental overflows in the event of amalfunction of the primary liquid level sensing means.
 76. The apparatusof claim 75, wherein said secondary liquid level sensing means comprisesa pair of short fixed electrically conductive probes extending to saidpredetermined level in said server container when said support housingis mated to the upper opening of the server container.
 77. A method fordetecting a level of a surface of a liquid in a container having anupper opening, the method comprising the steps of: providing a supporthousing moveable between an upward unlocked position and a downwardlocked position, said support housing being adapted to mate with theupper opening of the container in said downward locked position;providing a liquid level sensing means mounted in said support housingfor non-intrusively measuring the level of the surface of the liquid inthe container; intermittently providing power to at least a portion ofthe liquid level sensing means such that the liquid level sensing meansoperates periodically.
 78. The method of claim 77, wherein said liquidlevel sensing means comprises an optical sensor device mounted in saidsupport housing for non-intrusively measuring the level of the surfaceof the liquid in the container, said optical sensor device including alight emitting device for projecting incident light on the surface ofthe liquid in the container, and a light detecting device for detectingsaid incident light reflected from the surface of the liquid in thecontainer, and said step of intermittently providing power to the liquidlevel sensing means comprises: intermittently providing power to thelight emitting device such that the light emitting device operatesperiodically, whereby the liquid level can be detected periodically. 79.The method of claim 78, wherein said step of intermittently providingpower to the liquid level sensing means further comprises monitoring thephototransistor only when power is provided to the light emittingdevice.